They Used To Date
by OnlyMyThoughtsForCompany
Summary: "Yeah, you know they've known each other since the academy." "They used to live together." "Oh and they used to date." Or the one where Mills finds out something very surprising about the two Lieutenants of 51.
**Setting:** Season 1

 **Warnings:** None

 **Prompt:** None

 **Point Of View:** Third

 **Disclaimer:** Looks familiar? Don't own it.

* * *

"I just don't get it."

Peter was staring. Or he was trying really hard not to. For the first time in a long time Pete was able to just sit for a minute. Normally at this time he would be hastily preparing lunch for the entire house by himself, or otherwise would be on a call, after which he would have to get lunch ready. But today the two Lieutenant of House 51 had offered to cook, giving Pete ample time to observe as he had been doing all week. There was something about the two men's frankly bipolar relationship that confused the hell out of him. Not an hour ago Casey and Severide had been arguing so loudly that they'd had to be called into Boden's office to sort it out and now they were joking around and shoving each other halfheartedly as they worked around each other in the kitchen. Pete continued to watch covertly from the table as Casey ribbed Severide mercilessly about his cooking skills. Or rather lack thereof.

"What are you babbling about, Mills?" Herrmann barked.

Peter blinked in surprise, having been sure that no one had heard his mumbling. He glanced around to see he had most of the tables attention. Herrmann, Mouch, Shay and Dawson were all watching him expectantly.

"It's just…" he waved his hand towards the Lieutenants. "One second they're at each other's throats, the next, it's like they're best friends."

The groups eyes followed his hand.

"Ah, Casey and Severide have known each other a long time," Mouch said knowingly.

"Really?" Peter asked incredulously. He couldn't believe that, what with the way the two Lieutenants acted around each other.

"Yeah," Herrmann sighed. "And that means they think they're allowed to act like total idiots to each other."

"Yeah, you know they've known each other since the academy," Gabriela supplied.

"They used to live together," Shay added.

There was a beat of silence.

"Oh and they used to date," Mouch finished.

Mill's head whipped around so fast, a pain shot through his neck. "What?" His gaze snapped back to the men, who were now bent over inspecting a pot of sauce, faces an inch apart.

"But Lieutenant Casey was with Hallie… And Lieutenant Severide is always taking girls home from the bar…"

Shay huffed out an irritated breath. "Men, always thinking that you can only like one thing."

"Wait, so you're saying…" Pete trailed off awkwardly.

"Casey's bi," Dawson said, when it was obvious he wasn't going to continue.

"I'm not so sure about Severide though," Herrmann said glancing over at the kitchen. "It's never come up."

"Severide's pansexual," Shay put in helpfully.

"There you go, Mills."

"But wasn't Casey with Hallie for 8 years. So when were they together?"

"Well, it was more like 4 years with Hallie, what with their on-again-off-again thing."

"Yeah, so when it wasn't Casey and Hallie it was Severide and Casey."

Pete continued to gape at the group's calm demeanour until Mouch reached over and closed his mouth for him. He had just opened his mouth, no doubt to ask another question when a loud ruckus from the kitchen had them all glancing over. An extremely red-faced Severide was sporting a sauce splattered t-shirt while Casey slumped over the counter beside him, shoulder's shaking with laughter. Grimacing, Severide swiped a hand through the mess on his shirt and flicked it at Casey, spattering the red sauce all over his blonde hair. With an enraged grunt Casey shot up and launched himself at the other Lieutenant and they were off, shoving each other, wrestling good naturedly, knocking pans and dishes as they went.

Shaking his head with a fond smile, Herrmann yelled out to the pair, "Oi, Tweedledee and Tweedledum, you let our lunch burn and I don't care how high and mighty you are, I'll make you clean this house top to bottom, just like when you were Candidates."

The two froze in their stance, clutching each other's shoulder, identical grins off mischief on their faces and Pete was struck oddly by how much younger they looked when they were like this. How much freer they looked.

"Haven't been called that in a long time," Severide grinned and pulled Casey into a headlock. "Remember when we got called that every other day, Case?"

Casey pulled himself free with a jerk. "Hard to forget," he replied, trying to tame his blonde locks which were sticking up in ten different directions.

"Yeah well, you two were little troublemakers."

Severide threw an arm around the shorter man's shoulder and hauled him closer. "Don't know what you're on about Herrmann. You were laughing as much as anyone when we glued Mouch to the couch cushions."

The group, excluding Mouch burst into laughter, either at the memory or the picture the story conjured up.

"Just for the record, I wasn't and still am not amused by that story," Mouch declared reproachfully.

Everyone exploded into chatter all over again, laughing and talking each other, Herrmann regaling another story from Casey and Severide's youth so it was only Pete still watching the Lieutenants, who noticed the way Severide's eyes followed Casey as the younger man pushed away to check on the food.

* * *

The last shift of the week, ended with a bang, in the form of a small but deadly house fire. It was nowhere the biggest House 51 had ever seen but still it moved quickly to the structure of the building so there was a collective breath of relief when the last resident was accounted for and Boden called for evacuation.

Pete watched from the truck as each of his brother's staggered from the building, mentally counting each one until there was only one who hadn't exited.

Obviously following the same train of thought as Mills, Boden barked into the radio, concern colouring his voice, "Casey, where are you?"

Pete glanced sideways and caught Severide's eyes seeing the same concern he felt reflecting in the pale orbs. "He was right behind me…" the Squad Lieutenant trailed off, seeming unsure of himself for the first time and glanced back at the entrance of the building.

The house groaned pathetically as it was ravished by the roaring fire, catching everyone's attention.

"Casey," Boden growled.

Finally Casey's voice crackled back through the radio, the whole of House 51 shifting closer to hear the tinny words that were almost swallowed by the sounds of the fire, "I'm good Chief, got held up by some falling debris. I'm on my way out now."

Mills let out a visible breath of relief, the cold air whitening it, and slumped back against the truck. His eyes remained trained on the front door with the rest of the House, waiting for their Lieutenant to appear. The only one who didn't seem to relax was Severide, who remained tense and his stiff, hands, Pete noted, were clenching and unclenching around the helmet in his hands.

Another minute passed but to all the firefighter's waiting it felt like it could have been an hour. Severide shifted for the millionth time and looked to the Chief imploringly, Mills staring between them. Severide had already asked three time to go in and get Casey but had been denied every time. Boden listened to the protesting creaks that the house was making, cursed under his breath and pulled his radio in closer to check in again.

"Chief-"

Mills glanced at the Lieutenant again; his hair, damp with sweat was plastered to his forehead, his eyes were wide and wild and he was moving from foot to foot with feverish kinetic energy.

"No, Severide. We will wait until we hear from him again or-"

The chief was cut off by an agonising shriek as half of the top floor collapsed to the ground and clouds of black smoke billowed from the front door. The firefighter's shot to attention, many taking steps towards the building, but a stern "no" from their chief had them stopping in their tracks and glancing back uncertainly, none alright with leaving their Lieutenant in the wreckage. Only one man didn't stand down. It took Capp, Mills and Hadley's combined strength to drag Severide back but still he didn't let up, straining towards the orange blaze.

"Matt!" Severide yelled in a voice broken by fear.

"Severide, I will not send anymore men in there to die. Casey wouldn't want that."

Mills struggled to hold back the man as he turned on the chief. "You told me to wait and now he's trapped in there!" hissed Severide, contempt and dread filling him.

The Chief offered no words in his defence and merely turned back to his radio where he continued calling urgently for his fallen Lieutenant. Fifteen long, torturous seconds passed by and it occurred to everyone who was still thinking reasonably that Casey's PASS alarm hadn't gone off yet, meaning that he was at least moving in some sort of capacity.

The night went silent, even the sound of the crackling fire seemed to die down and all that was left was Severide's ragged breathing. Then the smoke parted and a familiar figure stumbled forward. The relief in the air was practically tangible as the truck and squad members of House 51 sagged back against the cherry red of their trucks. The engine firefighter's shot into action however now that they had the all clear to dowse the flames. Mills slowly let his hands slip from the Squad Lieutenant's shoulders, the only man who hadn't moved since the appearance of Casey.

Casey walked closer, pulling the helmet from his head and running his free hand through his sooty hair, he nodded an acknowledgment at the Chief. Severide finally seemed to come back to himself because he shrugged the remaining hands off roughly and strode forward, gaining the attention of every firefighter present. They watched open-mouthed as Severide stalked forward and with nothing more than a growled "fucking idiot" grabbed the lapels of Casey's jacket and yanked him forward, smashing their lips together.

For a moment, it seemed like nobody knew quite what to do including Casey, who simply stood there in shock, but then he dropped his helmet with a dull thud and slid his arms up around Severide's neck holding him close, ignoring the sudden chorus of clapping, cheering and wolf-whistling.

"Alright men, move it, this stuff isn't going to put itself away," the Chief ordered, the smile on his face betraying his stern facade.

Mills, rooted to the spot was left watching the pair as the rest of the team was spurred into action. The two had finally parted from their passionate embrace but only far enough for Severide's to bury his face into Casey's neck. The latter's mouth hovered near the former's ear, shaping quiet words that Pete couldn't quite make out.

He was only jolted out of his stupor when Herrmann walked past laughing and shaking his head, "About bloody time those two got their act together." He clapped his hand on Pete's shoulder and pushed him into action. "Let's move, Mills."

Boden ducked his head with a low chuckle and watched the two Lieutenants finally part before tipping his head back and calling to his men, "Alright, let's go home."


End file.
